1. Field of the Invention
This invention relates to an evaporative fuel-processing system for internal combustion engines, and more particularly to an evaporative fuel-processing system which is capable of detecting abnormality of the system itself.
2. Prior Art
Conventionally, an evaporative fuel-processing system for an internal combustion engine having a fuel tank and an intake passage has been widely used, which comprises a canister for temporarily storing evaporative fuel generated from the fuel tank, a purging passage communicating between the canister and the intake passage, and a purge control valve arranged in the purging passage for allowing evaporative fuel to be properly purged into the intake passage.
To check for a leak of evaporative fuel from the fuel tank, the canister, a passage connecting them, the above-mentioned purging passage, and other parts of the system, the following techniques have been proposed:
International Publication No. W091/12426 of PCT/DE/91/00010 proposes to provide pressure-detecting means for detecting pressure within the evaporative fuel-processing system, and an air admission control valve in an air inlet passage of the canister for control of admission of air into the canister, and determine that the system is normal if negative pressure can be created within the evaporative fuel-processing system by opening the purge control valve while closing the air admission control valve.
Further, Japanese Provisional Patent Publication (Kokai) No. 4-362264 proposes to detect abnormality of the evaporative fuel-processing system by negatively pressurizing the system, and then closing the purge control valve so as to monitor a change in pressure within the system over a predetermined time period.
However, in these evaporative fuel-processing systems for internal combustion engines, negative pressurization is performed of the whole system, and hence it is impossible to detect location of a faulty part.
Further, since operating conditions of the engine are not taken into account, it can be erroneously determined that there is leakage of evaporative fuel when there is no actual leakage thereof, or vice versa, depending on operating conditions thereof.